1. Field of the Invention
This invention relates to a fluorescent display device which effects luminous display of letters, images and the like, and more particularly to a fluorescent display device which selects picture cells to be illuminated by driving a pair of adjacent control electrodes.
2. Description of the Prior Art
A variety of display units including a cathode ray tube, a liquid crystal display device, a fluorescent display device and the like have been conventionally used to display letters, figures, images and the like. These display units are desirable to be thin and exhibit high resolution. In the fluorescent display device which is inherently advantageous in low power consumption, good visibility, a thinner shape and the like, much efforts have been made in order to obtain a display with high resolution.
FIGS. 4(a) and 4(b) show a general structure of fluorescent display device which includes control electrodes, each pair of adjacent control electrodes being concurrently selected and driven.
The fluorescent display device shown in FIGS. 4(a) and 4(b) includes an insulating substrate 1, strip-like anodes 2 arranged on the substrate 1 so as to extend in parallel to each other and a phosphor 3 deposited all over each of the anodes 2. In addition, insulating spacers 4 are arranged on the substrate 1 so that control electrodes 5 may be supported in a manner to be crossedly stretched above the anodes 2. Sections of the anodes interposed between each adjacent two control electrodes 5 each form a picture cell P. Each of the control electrodes 5 is connected at one end thereof to an electrode terminal 6 formed on the substrate 1. Above the control electrodes 5 are arranged filamentary cathodes 8 which serve as an electron source for emitting electrons. The fluorescent display device also includes a casing 9 formed of a transparent material, which is hermetically sealed on the substrate 1 by means of a frit glass 7 to form a vacuum envelope. The anodes 2 and cathodes 8 are connected to terminals (not shown) provided at the outside of the envelope. The fluorescent display device thus constructed is driven by applying a display signal to each of the anode electrodes 2 and energizing the respective pairs of adjacent two control electrodes 5 in order synchronous with the application of the display signal to the anode electrode. This causes the picture cells P to give off light emission so as to effect a desired display.
Operation of the fluorescent display device will be described in detail with reference to FIG. 5 which shows a drive circuit for the fluorescent display device shown in FIG. 4.
In FIG. 5, control electrodes of odd number 5.sub.1 -5.sub.n-1 are connected to an output section of a first control electrode drive circuit 102 and control electrodes of even number 5.sub.2 -5.sub.n are connected to an output section of a second control electrode drive circuit 103. The control electrode drive circuits 102 and 103 may be constructed in a manner known in the art, such as, for example, a shift registor. Anodes 2.sub.l -2.sub.m are connected to an output section of an anode drive circuit 101. The anode drive circuit 101 may be constructed in a manner known in the art which comprises a shift resistor acting as an input section and a latch acting as the output section which are connected together in series. A timing control circuit 104 serves to control timing of the control electrode drive circuits 102 and 103 and anode drive circuit 101. The timing control circuit 104 supplies complementary clock pulses CP.sub.1 and CP.sub.2 to clock input terminals of the control electrode drive circuits 102 and 103, respectively, and also supplies a timing pulse TP to the anode drive circuit 101. To an input section of the anode drive circuit 101 is supplied a display signal indicating a letter, an image or the like.
FIG. 6 is a timing chart of the circuit shown in FIG. 5.
Operation of the circuit shown in FIG. 5 will be further described with reference to FIG. 6.
When the complementary pulses CP.sub.1 and CP.sub.2 are generated from the control circuit 104 at a time t.sub.0, the control electrode drive circuit 102 supplies a signal of a high level to the control electrode 5.sub.1 in response to a rising edge of the pulse CP.sub.1. Then, at a time t.sub.1, the control electrode drive circuit 103 supplies a signal of a high level to the control electrode 5.sub.2 in response to a rising edge of the pulse CP.sub.2. In synchronism with selective driving of the control electrodes 5.sub.1 and 5.sub.2 at the same voltage of a high level, the anode drive circuit 101 supplies a signal corresponding to a display signal Vs to the anodes 2.sub.1 -2.sub.m. This causes parts of picture cells P.sub.11 -P.sub.1m corresponding to the display signal Vs to emit light so as to complete a display of a first row. At a time t.sub.2, the control electrode drive circuit 102 supplies a signal of a high level to the control electrode 5.sub. 3 in response to a rising edge of the clock pulse CP.sub.1, thereby the control electrodes 5.sub.2 and 5.sub.3 maintaining the same voltage of a high level are selected. In synchronism with such selection, a signal corresponding to a display signal Vs on a second row is supplied through the anode drive circuit 101 to the anodes 2.sub.1 -2.sub.m, thereby the corresponding parts of the picture cells P.sub.2l -P.sub.2m give forth light emission. In a similar manner, the remaining picture cells are selectively driven for light emission so as to effect a display of an image or the like.
In the fluorescent display device selectively driven the respective pairs of adjacent control electrodes in order at high level signals of the same voltage, a display with high resolution is effected by forming each control electrode using a fine wire and arranging the control electrodes at narrow intervals so that intervals between adjacent picture cells may be narrow.
However, this results in intervals between the control electrodes to be equal to those between the picture cells. Thus, arrangement of the picture cells at intervals as small as 0.2 mm or less causes short-circuiting and a failure in insulation between adjacent control electrodes. An attempt to solve such a problem in the manufacture of the fluorescent display device requires a great deal of skill in the manufacture and assembly of the control electrode and the assembly of the fluorescent display device, and causes deterioration of yield in the manufacture.